Funds are requested to carry out a development of immunochemically sensitive field effect transistor (IMFET). The theoretical analysis of a probe which would translate an immunochemical information directly into a measurable electrical signal has been performed. The size and nature of the reacting species (antibodies and antigens) precludes any mechanism in which these species must penetrate into the bulk of a solid phase in order to generate a measurable potential. Mainly for this reason, a direct reading immunochemical sensor must be based on surface reaction. A field effect transistor is ideally suited for a direct measurement of surface charge as we have shown in our preliminary work. The convalently immobilized antibody (or antigen) on the surface of the transistor then provides a highly specific binding site for the species to be measured. We are proposing to use insulin and guinea pig antibody to insulin as a model systme on which the sensitivity, reversibility, speed of response, and selectivity would be tested. The first major medical application of IMFET will be the study of infections in infants caused by Group B streptococcus.